It's not as simple as you make it seem! After installation, you still need to edit your DocumentRoot, enable mod_php, maybe set up a virtual host, maintain which document on your machine corresponds to which port on your machine, ...
Your scenario of running a simple test.php from the default DocumentRoot is a very contrived one, one that only the very first beginner will ever use, and even then only because he doesn't know how to configure Apache. Plus it assumes a lot of things: that it's on Linux, that it uses the distro-supplied packages, that they use a setup that is the very basic one, ... OK for beginners, but serious friction ('friction', not 'unsolvable problem' - that still doesn't make it unworthy of being addressed) for many experimentation scenarios.
sorry, but from scratch (no apache, no mysql, no php) to running 2 php/mysql sites in different virtual hosts takes less than 10 minutes on a modern ubuntu box (and probably most of the time will be spent configuring the site, not the servers). plus, i don't want to run a php -something in a shell each time i want to test something. also, while modern ORM's abstract away most of the database , I still wouldn't use sqlite on the dev machine for a site which will run on mysql in production
Your scenario of running a simple test.php from the default DocumentRoot is a very contrived one, one that only the very first beginner will ever use, and even then only because he doesn't know how to configure Apache. Plus it assumes a lot of things: that it's on Linux, that it uses the distro-supplied packages, that they use a setup that is the very basic one, ... OK for beginners, but serious friction ('friction', not 'unsolvable problem' - that still doesn't make it unworthy of being addressed) for many experimentation scenarios.